<html>
<script>
function isNoEmail(str){
     var strartu=str.lastIndexOf("@"); 
     var sdown=str.indexOf("@");
     var isNostr=str.substring(str.lastIndexOf("@") + 1,str.length);
     var stu=isNostr.lastIndexOf(".")+1; 
     var sdn=isNostr.indexOf("."); 
     if(strartu =='-1'||stu=='-1'){
     	return false;
  	}
     if(strartu==sdown&&stu!=sdn)
    	{
     	return true;   
  	}else{
     	return false; 
  	}	
  }

console.log(isNoEmail("a.le@163.com"));
console.log(isNoEmail("a@163.com"));
console.log(isNoEmail("jerry.wang@163.com"));
console.log(isNoEmail("a163.com"));
console.log(isNoEmail("a@b"));
</script>
</html>